The present invention relates to an underwater hydraulic coupling. More particularly, the invention relates to a hydraulic coupling which includes a pressure bleed device for venting excess pressure from the hydraulic line to which the coupling is connected.
Hydraulic couplings are commonly used to functionally connect separate lengths of hydraulic transmission lines. Such couplings generally include a male component which comprises a cylindrical probe and a female component which comprises a cylindrical receptacle into which the probe is inserted. Each of the male and female components typically also comprises a spring-loaded poppet valve that seals against a corresponding valve seat and a valve actuator in the form of a nose or a stem that extends longitudinally from the poppet valve. Thus, when the male and female components are connected together, the valve actuators will push against each other and force the poppet valves away from their respective valve seats to thereby allow fluid to flow through the coupling. In order to prevent hydraulic fluid from leaking into the environment, one or both of the male and female components may comprise a number of environmental seals for sealing between the probe and the receptacle.
Hydraulic couplings of this kind are often used in conjunction with underwater devices which are employed in the production of oil or gas from subsea wells. In addition, the male and female components of the couplings are usually attached to opposing plates of a manifold so that several couplings may be connected and disconnected simultaneously. In this regard, the plate to which the female components are attached is often rigidly connected to a subsea structure, while the plate to which the male components are attached is detachable so that it may be brought to the surface. Furthermore, in order to prevent an efflux of hydraulic fluid during separation of the male and female components, the couplings are designed such that the poppet valves will close before the environmental seals are disengaged.
When the male and female components are disconnected from each other, hydraulic pressure may become trapped in the lines to which these components are connected. If the hydraulic pressure is trapped subsea, the settings of the valves throughout the hydraulic system may be disrupted, which may result, for example, in failsafe-type valves being prevented from moving to the failsafe position. It is therefore desirable to bleed the hydraulic lines to relieve this trapped pressure. However, bleeding the lines may also allow seawater to enter the hydraulic system, which is undesirable.
In U.S. Pat. No. 5,365,972, an underwater hydraulic coupling is described in which at least one of the male and female components comprises a bleed passage which extends through the poppet valve and the valve actuator. To prevent the ingress of seawater, the component includes a second poppet valve which faces in the opposite direction of the main poppet valve. These two poppet valves are coupled together such that, when the actuator pushes the main poppet valve open, it also forces the second poppet valve to open. After the main poppet valve is closed, if overpressure is present in the hydraulic line, the second poppet valve will open against the force of a spring and thus allow the hydraulic pressure to escape through the bleed passage.
However, this coupling is relatively complicated and comprises several fine-tolerance components which may have an increased risk of failure. Also, the proper operation of this design relies on the balancing of a number of springs, which may result in the failure of the coupling if the springs are not properly tuned. In addition, the bleed passage will allow sea water to enter the coupling even when the main poppet valve is closed. This can lead to corrosion and scaling of the poppet valves, which may further deteriorate the function of the coupling.